Examinando por Autor "Antunes, Fernando Ventura"

Mostrando 1 - 8 de 8

Characterisation of fatigue crack growth using digital image correlation measurements of plastic CTOD.
(Elsevier, 2019-03-27) Vasco, José Manuel; Diaz-Garrido, Francisco Alberto; Antunes, Fernando Ventura; James, Neil
Crack tip opening displacement (CTOD) was measured using digital image correlation (DIC) and resolved into elastic and plastic CTOD components via an offset compliance technique. The plastic CTOD range gave a single linear correlation for fatigue crack growth rate at stress ratios of 0.1 and 0.6 in compact- tension (CT) specimens of Grade 2 titanium. A sensitivity analysis was performed to find the optimum position in the crack wake to make the CTOD measurements. The results are the first time (to the authors knowledge) that plastic CTOD has been found directly from experimentation and demonstrate that plastic CTOD is a useful alternate characterising parameter for fatigue crack growth to the stress intensity factor defined by Irwin.
Effect of crack flank holes on fatigue crack growth
(Elsevier, 2023-01-07) Neto, Diogo Mariano; Cavaleiro, Nuno; Sérgio, Edmundo; Jesus, Joel de; Camacho-Reyes, Alonso; Antunes, Fernando Ventura
The effect of drilling two symmetric holes along the crack flanks on the fatigue crack growth (FCG) rate was evaluated numerically. The FCG increases (decreases) when the crack tip is behind (ahead) the holes. This behaviour is enlarged both by increasing the diameter of the holes and by reducing the distance between them. This is consequence of the geometrical effect, which modifies the plastic zone size. Experimental work validated the numerical model, indicating that that cumulative plastic strain at the crack tip is an adequate crack driving force and that cyclic plastic deformation is the main damage mechanism of FCG.
Experimental analysis of the plastic CTOD to characterize the variable amplitude fatigue crack growth in Grade 2 titanium samples
(Elsevier, 2023-05-23) Gómez-Gonzales, Giancarlo Luis; Vasco, José Manuel; Antunes, Fernando Ventura; Neto, Diogo Mariano; Diaz-Garrido, Francisco Alberto
In this paper, the plastic component of the crack-tip opening displacement (CTODp) is experimentally evaluated to characterize the fatigue crack growth behavior in a Grade 2 titanium sample under single overload with constant amplitude loading conditions. The CTOD measurements were performed with the 2D-Digital Image Correlation (DIC) technique. The experimental results show a linear correlation between CTODp and fatigue crack growth rates, suggesting the independence of this relationship to load-interaction effects. Therefore, this study demonstrates that the CTODp can be a suitable crack-driving parameter to study crack propagation behavior under variable amplitude loading. Furthermore, it suggests that the fatigue crack growth process is primarily caused by cyclic plastic deformation.
Experimental evaluation of plastic wake on growing fatigue cracks from the analysis of residual displacement fields
(Wiley, 2022-02-19) Vasco, José Manuel; Diaz-Garrido, Francisco Alberto; Camacho-Reyes, Alonso; James, Neil; Antunes, Fernando Ventura
A growing fatigue crack gives rise to a plastically deformed wake of material that envelops the crack. In this work, the plastic wake extent during fatigue crack growth is experimentally quantified by analyzing the crack tip displacement fields measured with digital image correlation. A novel technique based on use of a yield criterion is proposed that uses the undamaged state of the specimen as the reference state in the image processing. The plastic wake was identified by differentiation of the residual displacement fields obtained with a near-zero load level to avoid any rigid body motion. The plastic wake extent was then found by assuming that the boundary between the elastic and plastic regions would occur when the equivalent stress was higher than the yield stress of the material. The results presented can contribute to a better understanding of the mechanisms driving fatigue crack propagation.
Limitations of small-scale yielding for fatigue crack growth
(Elsevier, 2021-05-28) da-Silva-Veloso-Marques, Bruno Miguel; Borges, Micael Frias; Antunes, Fernando Ventura; Vasco, José Manuel; Diaz-Garrido, Francisco Alberto; James, Neil
The work described here has led to a simple criterion that defines the boundary of the small-scale yielding, SSY, regime to avoid invalid use of the LEFM parameter, ΔK, as the characterising parameter for fatigue crack growth rate. The approach proposed is based on the analysis of crack tip opening displacement, CTOD, and its separation into elastic and plastic components. SSY conditions are shown to dominate when the elastic component of CTOD is >75% of the total CTOD measured at a distance of 8 μm (the finite element mesh size) behind the crack tip, i.e., Δδe/Δδt > 75%. Large-scale yielding, LSY, conditions become dominant for relatively large values of plastic CTOD, Δδe/Δδt < 60%. An increase in crack length (and therefore of ΔK), a decrease in yield stress of the material and the existence of plane stress conditions all promote LSY. The results obtained from various loading and geometric conditions simulated in this work demonstrate that caution should be used in assuming that the use of ΔK is valid even for high strength alloys like Ti6Al4V. In this material, the boundary of the elastic regime was crossed and SSY conditions lost, for the longest crack lengths studied and in the case of overloads.
Numerical analysis of compliance and fatigue life of the CCC specimen
(Elservier, 2023-01-23) Neto, Diogo Mariano; Antunes, Fernando Ventura; Sérgio, Edmundo; Branco, Ricardo; Camacho-Reyes, Alonso; Díaz-Garrido, Francisco Alberto; Gómez-Gonzales, Giancarlo Luis; Vasco, José Manuel
This study presents the numerical evaluation of the compliance in the CCC specimen aiming to assess the crack length inside the specimen. The numerical model considered the elastoplastic behaviour of the specimen, which is modelled using axisymmetric finite elements. The results shown that the propagation of the crack yields a nonlinear increase of the compliance. Nevertheless, variation of the compliance is very small for small values of crack radius. Considering a loading sequence composed by four load blocks of constant amplitude, the fatigue crack growth was predicted both using the Paris law and the numerical model. Both predictions agree but only the numerical simulation is able to capture the crack retardation between load blocks
On the experimental characterisation of crack tip displacement fields on nonplanar elements: Numerical and experimental analysis
(Elsevier, 2023-02-04) Camacho-Reyes, Alonso; Antunes, Fernando Ventura; Vasco, José Manuel; Diaz-Garrido, Francisco Alberto; Felipe-Sesé, Luis
In this work, a numerical and experimental study about crack tip fields characterisation on curve-cracked elements has been performed. This study combines a novel differential geometry approach combined with 3D-DIC and FEA results to determine crack-tip parameters from the displacement field on a curved cracked element. The work aims to validate and compare some aspects that cannot be addressed using 3D-DIC. SIFs for different crack lengths are determined using DIC and FEA data and compared In addition, a comprehensive comparison between experimental and numerical fields is done using an Image Decomposition technique based on Tchebichef polynomials.
Plastic CTOD as fatigue crack growth characterising parameter in 2024-T3 and 7050-T6 aluminium alloys using DIC
(Wiley., 2020-03-03) Vasco, José Manuel; Diaz-Garrido, Francisco Alberto; Antunes, Fernando Ventura; James, Neil
The plastic range of crack tip opening displacement (CTOD) has been used for the experimental characterisation of fatigue crack growth for 2024-T3 and 7050-T6 aluminium alloys using digital image correlation (DIC). Analysis of a complete loading cycle allowed resolving the CTOD into elastic and plastic components. Fatigue tests were conducted on compact tension specimens with a thickness of 1 mm and a width of 20 mm at stress ratios of 0.1, 0.3 and 0.5. The range of plastic CTOD could be related linearly to da/dN independent of stress ratio for both alloys. To facilitate accurate measurements of CTOD, a method was developed for correctly locating the crack tip and a sensitivity analysis was performed to explore the effect of measurement position behind the crack tip on the CTOD. The plastic range of CTOD was demonstrated to be a suitable alternate parameter to the stress intensity factor range for characterising fatigue crack propagation. A particularly innovative aspect of the work is that the paper describes a DIC-based technique that the authors believe gives a reliable way to determine the appropriate position to measure CTOD.

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Examinando por Autor "Antunes, Fernando Ventura"